Resistive device and method of making



Dec. 24, 1946. c. J. GANCI 2,413,043

RESISTIVE DEVICE AND METHOD OF MAKING Filed Aug. 14, 1943 INVENTOR.

w 07-709mm Patented Dec. 24, 1946 RESISTIVE DEVICE AND METHOD OF MAKING Charles J. Ganci, Rldgewood, N. Y., assignor to Ward Leonard Electric Company, a corporation of New York Application August 14, 1943, Serial No. 498,651

6 Claims. 1

This invention relates toimprovements in resistive devices such as tubular resistive units and other forms.

In making resistive units, such as of tubular form, in which a solid conductor, usuall in the form of a wire or ribbon, or a conductor of various forms and cross-sections, is utilized as the resistive conductor, it is desirable to provide stranded wire connections thereto, or so-called pigtail leads, owing to their flexibility and convenience in making connections to the circuit in which the device is to be used and owing to their comparative freedom from breakin after repeated bending and twisting. It has been common to twist the stranded wire around the solid wire and solder the connection but this forms an objectionably enlarged joint; and particularly in resistive units wherein the resistive conductor is coated with an insulating coating, the enlarged joint is objectionable not only in increasing the outside dimension of the unit but in the difficulty of properly covering and embedding the joint with the insulating coating.

According to the'present invention, the ends of the conductors are butt welded together to produce a joint not appreciably larger than the size of the conductors and give the joined conductors the appearance of a continuous conductor. When a resistive conductor with such welded terminal leads of stranded wire is utilized in a resistive device, there are no enlarged joints to contend with in applying the insulating coating, resulting in a final product having a uniform and smooth appearance throughout. But the butt welding of the end of a stranded wire cannot be accomplished properly if it be attempted to weld by joining the ends of the stranded wire to the end of a conductor; because some of the strands may be welded while others will not. This results in a poor electrical connection and in the spreading out of the unwelded strands or of some of them, giving an awkward joint to properly and fully cover by the insulating coating. It also results in a portion protruding from the unit at the joint. Furthermore, during the maturing of the insulating coating, as by firing in a furnace, the strains imposed on the few welded strands are likely torupture the connection, giving an open circuit in the completed article. The number of rejects from this cause alone may be considerable. Even if the opening of the circuit does not occur, the few strands remaining connected will, during use of the device, cause excessive heating localized at the joint which is likely to cause a breakdown of the device after a short period of use. The present invention overcomes these various difllculties.

One object of the invention is to produce a resistive device which will be durable and dependable in long continued use. Another object is to obtain a, device which will have a uniform and smooth surface throughout its length and substantially overcome rejects in the process of manufacture due to failure of the connection between the conductor and the stranded lead wires. A further object is to produce a process of manufacture which may be conveniently accomplished and carried out with assurance of dependability and durability. Other objects and advantages will be understood from the following description and accompanying: drawing which illustrate embodiments of the invention and the steps in the method of making.

P18. 1 is a side view of a resistive device of tubular form showing the tubular support and the conductor applied thereto before the application of the insulating coating; Fig. 2 is a side view of the completed unit; Fig. 3 is a diagram showing a step in the process of preparing the stranded conductor for welding; Fig. 4 is a diagram showing a further step in the process; Fig. 5 is a similar diagram showing the final step in the process; and Figs. 6, 7 and 8 are side views of joined conductors as illustrative examples.

Referring to Fig. 1, the main support is a tube i of insulating material such as porcelain. On this is wound a solid conductor 2 forming the resistive conductor. This is of a proper size, length and. number of turns to give the desired resistance to the unit. It may be of any suitable metal or alloy, such as Nichrome composed of nickel, chromium and iron, or may be an alloy of nickel and copper, or of nickel and chromium, various alloys of iron, or any other metal or alloy according to particular requirements.

At each end of the resistive conductor 2 is a joint 3 between it and the stranded wires 4 and 5 forming the flexible terminal connections. The lead 4 continues from its joint 3 around the tube and then passes within the tube through a hole 6 and then out from the end of the tube to form the outside lead. The lead 5 continues from its joint 3 around the tube and then passes within the tube through a notch l and through the length of the tube to form the other outside lead.

As to the joint 3, it is shown as a solid connection between the solid conductor 2 and the stranded wire leads 4 and 5; and this joint is no larger than the conductor 2 or the leads, giving the appearance of a continuous conductor of uniform size having no protruding portions or objectionable enlargement. joint which may be readily and conveniently cov-' ered by the insulating coating. In fact it is just as easily and fully covered as any other portions of the conductor. The device as shown in Fig. 1

is ready for the application of the insulating coating which may be of any suitable material but is preferably of vitreous enamel material. The coating is matured by flring in a fur- It therefore forms a nace if of vitreous enamel, and by drying or other'wiseaccording to the character of the coating material.

Fig. 2 shows the completed unit with the in-,

sulating coating 8; and it is obvious that the device is of uniform size throughout with a smooth Y surface and no objectionable protruding portions.

This particular resistive unit was for an immension heater and was adapted closely fitted tube or casing; any projection from to slide into a quite the unit due to enlarged. joints or connections between the conductor and leads would prevent it from fittingwithinthe tubular casing. In making the unit, the resistive conductor is first made of proper length and then-the stranded wire terminalsare joined'fthereto' in the manner later described;fiThee-freeeiidof the lead 6 is passed through thehole s and then the inner portion of th lead 4 and the conductor; is wound around the tube and also a portion of the lead 5. The remaining portion of the lead 5 is then-passed through the length of the tube and held in place by being drawn into the notch l. The insulating' coating is thenapplied. r

As to-the making of the"joint,fEig'.'3shows' the first step. A length of stranded wire 9 is clampedbetween the jaws 10. of .a butt welder,

' a portion of the wire extending between the two The Ewelder is supplied with cursuitable source, such as from the pairs of fljaws. rent from a secondary!lofatransformer l2. The heating is concentrated at the midportion of the stranded of the wire to-form two separate leads and in a fused solid end [3 on each-of the leads, as shown in Fig. 4'; This solid fused end is not materially larger or smaller than thejsize or diameter of the stranded wire and all of the strands are per ends givinga solidjoint Messhown :in-Flggfifi and the (:onnection of :all-ofith-strands'tojithe mt or:

about the same "size "as xii-emerges 'orth ea solid conductor-is insured with fa 'sdlid'j support, a solid resistive conductor carried thereby, and a lead of a stranded conductorjoined gether and fused in the manner described with reference to Fig. 5. A stranded wire 35 thus fused to a larger braided wire 20 is'shown as an example in Fig. 8 at the solid joint 2 I. All strands of each of the two conductors are thus fused to the common joint and insure complete electrical connection between all strands of both conductors.

Although preferred embodiments have been described as illustrative examples, the invention may be embodied in other types and forms of resistive devices and modifications made without departing from the scope of the invention.

I claim: e 1. A resistive device comprising an insulating thereto, the end of the stranded conductor having a fused solid end butting against the end of the solid conductor and fused thereto in a solid joint of a size approximately equal to that of the larger of the two conductors.

2-. A resistive device comprising an insulating 'support;, a,-s,olid resistiveiconductor carried thereby, and a"l'e"ad"'of""a stranded conductor joined thereto, the endflof; each strand of the stranded oonductoribeing =fused'into1a:solidsend, and the 'said solid end beingfusedlto the" end of the solid conductor; a 1" 3; A resistive device comprising an insulating support, a solid resistiveconductor carried thereby, a lead of a stranded conductor joined therewire and fused there, resulting in the separation wires. Another stranded leadis "in'i il afly Q011 nect-ed td't'he other end'iioffthe lsolid conductor, 2; and the lj-combined conductor is ,then ready for applieationj to the tube 1 :the device being;

completed m'themannerzalready-described; ftion's of each ofv said stranded conductors;

This method of formingthe joint is applicable to the joining-ofstrandisdcondirctois, or'xnul tiple cond I difierent sizes massages ductors of shows a stranded conductor} actors. of different; sizes "to solidIcpn-j" Fig. 265

. bonnected..to...a,,

Solid ll' l t e. oi t H5. the,..wire; is being:

of much larger size than thestrandedwir'ei Fig.

'7 shows the stranded wire l5 connected at the joint 18 to a solid wire ldof smaller size. This method of forming the joint is applicable like- I wise to the joining of two stranded or braided wires or conductors. In. that'case a solid end'i first formed on the ends of each of such conductors in the manner described with reference to Figs. 3 and 4. The fused ends of the two conductors to be joined are then brought tosu porting u Y woundth'erjeo'n; a lead'i'of Estranded conductor joined to each-end of jsaidsolid i: -'-tively;:"tj he ends of the leaf fused tq solid"; ends,; and said: agairistfih' to, the fused solid end of the stranded conductor butting against the end of the solid conductor and fused thereto in a solid joint of a"'jsize-approximately equal to that of theilargeii of the two conductors, and an insulating coating covering said resistive conductor and'sla' id joint.

. 4. A resistive'device comprising; an insulating support, a solid resistive conductor-1 carried there, 'oine'd thereby, a lead of astranded conduct I to,'thejend of each strand of the stranded conductor being fused into a solid end, and the said solid end being. fused to the end oft-the solid con.

ductor, and an insulating .coating'fcoverihg said resistive conductor and said joint. r .5. A resistive device comprisingan insulating supporting tube, a solid resistive conductor wound f thereon, alead ofastrandedrconductor joined to each end -'of said solid conductor respectively, the

fusadsolidjehds of thesaid s'tranded conductor -buttingagainst the, ends'of 'saidsdlid conductor and fused thereto in solid joints of a size'fdpproximately' equal to the size of the larger ofjthe con- Eductors, and an insulating coatinggcovering said 'solidconductor and coveringsaid jeints porjii;v A resistive} device comprising an insulating a solid;- resistive conductor lductor respec- "s't Ii d wire being Lie mi butting "nds of said solid conductor and fused thereto in solid joints of a size approximately equal to the size of the larger of the conductors, and an insulating coating covering said [solid conductor and covering said joints and portions of each of said stranded conductors, the

uncovered ends of said stranded conductors being passed through openings in said tube to form external leads.

CHARLES J. GANCI. 

